1. Field of the Invention
The present invention relates in general to a hybrid drive system for driving a motor vehicle, which has an engine and a motor/generator as drive power sources, and more particularly techniques for starting the engine.
2. Discussion of the Related Art
There is known a hybrid drive system for a motor vehicle, which includes (a) an engine operated by combustion of a fuel, (b) a first motor/generator, (c) a distributing mechanism for mechanically distributing an output of the engine to the first motor/generator and an output member, (d) a second motor/generator whose rotary force is transferred to a power transmitting path between the output member and a drive wheel of the motor vehicle. An example of such a hybrid drive system is disclosed in JP-A-50-30223, wherein the distributing mechanism consists of a planetary gear device, and the rotary force of the second motor/generator is transferred to the output member. In this hybrid drive system, the first motor/generator is used exclusively as an electric generator to charge an electric energy storage device such as a battery with an electric energy, while the second motor/generator is used exclusively as an electric motor for driving the vehicle, either alone or in cooperation with the engine. Generally, an electric generator may be used as an electric motor, while an electric motor may be used as an electric generator. In this sense, the term "motor/generator" is used herein.
The above-identified publication JP-A-50-30223 does not refer to a manner of starting the engine.